MR-guided focused ultrasound with spatial and temporal temperature control for hyperthermia

Magnetic Resonance (MR)-guided Focused Ultrasound (MRgFUS) is a promising non-invasive method for controlling hyperthermia and local drug delivery. In this work, we developed a system capable of controlled tissue heating using proportional-integral-derivative (PID) feedback control combined with 7T MR thermometry for temperature feedback. MR thermometry was validated by an optical temperature probe. We have measured and simulated MR estimates of transient ultrasound-induced heating in a tofu phantom and performed controlled heating studies in an in vivo Met-1 mouse tumor. MR thermometry estimates agreed with fiber optic temperature measurements within 1°C, and simulations of heating in a tofu phantom were in agreement with the MR temperature measurement. MR-Acoustic Radiation Force Imaging (ARFI) was used to detect micron-scale displacement caused by acoustic radiation for beam localization in the absence of heating. The MRgFUS system developed here demonstrates adequate spatial and thermal accuracy for image-guided hyperthermia applications in small animals.